The present invention relates to a reflector structure for improving irradiation uniformity of a linear lamp array, and especially to a reflector structure for improving irradiation uniformity of a linear lamp array applied in a semiconductor process.
A rapid thermal process plays an important role in the semiconductor-manufacturing process. The temperature of a wafer increases very rapidly in the rapid thermal process by the infrared irradiation from a lamp array so as to grow an oxide layer, a polysilicon layer, or a source/drain region. There are many different kinds of rapid thermal processors, and each of them has a specific kind of lamp array, such as a linear lamp array, a circular lamp array, and a hexagonally honeycombed lamp array. The linear lamp array is formed by a plurality of linear lamps arranged in a direction perpendicular to its length. Since the irradiation intensity of each linear lamp is weak at its two end parts and is strong at its middle part, the irradiation uniformity of the linear lamp array is poor in the direction parallel to the linear lamps so that the temperature of the wafer can not increase evenly. However, in consideration of the production cost, the rapid thermal processor using a linear lamp array is still popularly used in some semiconductor factories.
FIG. 1 schematically shows a conventional thermal processor using a linear lamp array. The direction 4 is perpendicular to the linear lamp 2 on the plane of the linear lamp array, and the direction 5 is parallel to the linear lamp 2. Only the infrared irradiation from the front side (the side faced to the wafer 3) of the lamp array 2 can be received by the wafer 3, but the infrared irradiation from the back side (the side opposite to the wafer 3) of the lamp array 2 is wasted. Therefore, there is a planar reflector structure 1, such as a planar mirror, set on the back of the lamps for reflecting the infrared irradiation from the back side of the lamps 2 to the wafer 3.
FIG. 2 shows the irradiation intensity distribution in a conventional rapid thermal processor using a linear lamp array with the planar reflector structure along the direction 5. The length of each lamp of the linear lamp array 2 is 30 cm, the distance between the reflector structure 1 and the wafer 3 is 4 cm, and the distance between the linear lamp array and the wafer 3 is 2 cm. Since both the irradiation intensity of the infrared rays irradiated from the linear lamp array 2 and of those reflected from the reflector structure 1 are quickly weakened at its two end parts along the direction 5, the irradiation intensity of the total infrared rays received by the wafer is also quickly weakened at the two end parts. According to the theoretical estimation, a region, whose light intensity difference is less than 4%, has a temperature difference less than 1%, and is defined as an irradiation uniformity region. Therefore, the irradiation uniformity region of the conventional reflector structure is only 14 cm long under the middle part of the linear lamp array 2 along the direction 5. That is to say, if the diameter of the wafer increases, the length of the linear lamp and the size of the rapid thermal processor should greatly increase.
The conventional reflector structure also has been used in another rapid thermal processor having two sets of linear lamp arrays on the two sides of the wafer, arranged in two directions perpendicular to each other, so called xe2x80x9ccross lamp configurationxe2x80x9d. Although the irradiation uniformity is improved by using two sets of linear lamp arrays, the production cost and the size of the rapid thermal processor significantly increases.
It is specifically an object of the present invention to provide a novel reflector structure, which can improve the irradiation uniformity of a linear lamp array applied in a semiconductor process.
It is therefore an object of the present invention to provide a novel reflector structure such that the aforementioned limitations and difficulties encountered in the prior art can be overcome.
It is specifically another object of the present invention to provide a novel reflector structure such that the production cost can be significantly reduced.
It is specifically another yet object of the present invention to provide a novel reflector structure such that the size of a rapid thermal processor can be significantly reduced.
The reflector structure of the present invention includes a central reflector, two first side reflectors. The central reflector is horizontally set above the linear lamp array at a first predetermined distance from the wafer for reflecting light irradiated from a central part of the linear lamp array to a wafer. The two first side reflectors are horizontally set above the linear lamp array at a second predetermined distance from the wafer, wherein the second predetermined distance is less than the first predetermined distance, and respectively connected to two opposite sides of the central reflector for reflecting light irradiated from two side parts of the linear lamp array to a wafer. Note that the distance variation between the reflector and wafer is parallel to the linear lamps.
Preferably, the two first side reflectors are integrally formed to the two opposite sides of the central reflector, respectively.
According to the present invention, the reflector structure further includes two inclined reflectors respectively connected to one side of each of the two first side reflectors at an inclined angle to the wafer for reflecting light irradiated from two end parts of the linear lamp array.
Preferably, the two inclined reflectors are integrally formed to the one side of each of the two first side reflectors, respectively.
Preferably, the inclined angle is equal to 45xc2x0 or 30xc2x0.
According to the present invention, the reflector structure further includes two second side reflectors horizontally set above the linear lamp at a third predetermined distance to the wafer, wherein said third predetermined distance is less than the second predetermined distance, and respectively connected to one side of each of the two first side reflectors for reflecting light irradiated from two further side parts of the linear lamp array to a wafer.
The present invention may best be understood through the following description with reference to the accompanying drawings.